It is conventional to inject materials such as air into furnace baths via openings (or tuyers) located towards the bottom of the furnace. It is also known in steel making to direct oxygen into a furnace via axially mounted downwardly extending lances suspended above the bath. More recently it has been proposed to use a pyrometallurgical lance which can be lowered into the furnace bath from above. In such proposals the lances inject air or oxygen enriched air through an outer tube and in some processes, a fuel such as oil or coal through a concentric inner tube. Swirlers are located the lance to improve cooling of the outer wall. As the the lower end or tip of the lance is lowered into the furnace, slag resting on the top of the bath may splash on to the lance and freeze and adds further protection as the lance contacts with the bath.
Relatively small pilot plants having a capacity of 50 kg to 5000 kg have been described in which a lance of approximately 2-12 cm cross section is raised and lowered by a wire and pulley and stabilized by guy wires. However, such means would not be practical for a large scale plant with a lance of for example 30-45 cm diameter and being 10 meters long. When the lance tip is submerged the bath becomes intensely agitated. These lances require to be periodically repaired due to consumption of the lance tip. Problems have been encountered in trials involving maneuvering of such lances into and out of position as well as in raising and lowering the lance into the furnace. Because of the size and weight of the lance and space constraints typical of a furnace site, maneuvering a lance into and out of its mounting is intrinsically difficult and potentially hazardous. Replacement of one lance by another must be accomplished without delay. Moreover it has been discovered that if a 10 meter long lance is rigidly mounted as hitherto practiced with non submerged lances, stresses are introduced due to the intense agitation of the melt at the lower end of the lance and the lance fractures or the carriage and guides is damaged.
It has also been found that if too great a latitude of movement of the lance tip is permitted, the lance deflects the circulating bath flow causing increased wear on the lance itself, and introducing undesirable mixing of the bath. Furthermore, in situations of continuous feed and/or continuous or batch tapping it is necessary to control the height of the lance tip to ensure adequate oxygen transfer and temperature control of the bath.
It is an object of the present invention to provide improved means for raising and lowering a lance into a furnace.